Investigation of structural and reflective characteristics of short-period Mo/B4C multilayer X-ray mirrors.

The results of a study of the structural and reflective characteristics of short-period multilayer X-ray mirrors based on Mo/B4C at wavelengths 1.54 Å, 9.89 Šand 17.59 Šare presented. The period of the samples varied in the range 8-35 Å. The average widths of the interfaces were ∼3.5 and 2.2 Šat one and the other boundaries, with a tendency for weak growth with any decrease in the period. The interlayer roughness was ∼1 Å. The research results indicate promising prospects for the use of multilayer Mo/B4C mirrors for synchrotron applications.

EUV telescope for a Cubesat nanosatellite.

This paper describes in detail a compact (2U format) telescope operating in the extreme ultraviolet range for studying the solar corona at a wavelength of 17.14 nm. The telescope objective has been built according to the Ritchey-Chrétien scheme with the following parameters: effective focal length of 381.3 mm, field of view of 2×2∘, and angular resolution of 11 in. Reflective multilayer Al/Be coatings were used, having 55% reflectance and a 0.4 nm spectral bandwidth. The wavefront rms error is 30 nm. An interferometric technique for controlling the shapes of the substrates and for adjusting the optical system and detector of the telescope assembly is described in detail.

A concept of "materials" diffraction and imaging beamline for SKIF: Siberian circular photon source.

Over the next decade, the extremely brilliant fourth generation synchrotron radiation sources are set to become a key driving force in materials characterization and technology development. In this study, we present a conceptual design of a versatile "Materia" diffraction and imaging beamline for a low-emittance synchrotron radiation facility. The beamline was optimized for operation with three main principal delivery regimes: parallel collimated beam ∼1 mm beam size, micro-focus regime with ∼10 µm beam spot size on the sample, and nano-focus regime with <100 nm focus. All regimes will operate in the photon energy range of 10-30 keV with the key feature of the beamline being fast switching between them, as well as between the various realizations of diffraction and imaging operation modes while maintaining the target beam position at the sample, and with both spectrally narrow and spectrally broad beams up to the energy band ΔE/E of 5 × 10-2. The manuscript presents the details of the principal characteristics selected for the insertion device and beamline optics, the materials characterization techniques, including the simulations of thermal load impact on the critical beamline optics components. Significant efforts were made to design the monochromators to mitigate the very high beam power load produced by a superconducting undulator source. The manuscript will be of interest to research groups involved in the design of new synchrotron beamlines.

Correction: Depth-resolved oxidational studies of Be/Al periodic multilayers investigated by X-ray photoelectron spectroscopy.

Correction for 'Depth-resolved oxidational studies of Be/Al periodic multilayers investigated by X-ray photoelectron spectroscopy' by Niranjan Kumar et al., Phys. Chem. Chem. Phys., 2023, 25, 1205-1213, https://doi.org/10.1039/D2CP04778K.

Depth-resolved oxidational studies of Be/Al periodic multilayers investigated by X-ray photoelectron spectroscopy.

The quantification of surface and subsurface oxidation of Be/Al periodic multilayer mirrors due to exposure in the ambient atmosphere was investigated by depth-resolved X-ray photoelectron spectroscopy. The contribution of oxidation was lower for the thicker layer of Al in the periodic structures since the surface was less chemically reactive for the oxidation. This was investigated by finding the depth-resolved slope of the intensity ratio of metal/oxides (Be/BeOx and Al/AlOx) by analyzing the chemical shift of Al 1s and Be 1s photoelectrons. Furthermore, a well-resolved doublet chemical shift in the O 1s spectra indicated the formation of BeOx/AlOx and BeOH/AlOH oxides. The investigation showed that the subsurface and surface regions were dominated by metal-hydroxide (BeOH/AlOH) and metal-oxide (BeOx/AlOx) bonding, respectively, analyzed by the depth-resolved chemical shifts.

High-aperture low-coherence interferometer with a diffraction reference wave.

A high-aperture low-coherence interferometer with a diffraction reference wave based on a tipped single-mode optical fiber was proposed and investigated. Due to the usage of the central least-aberrated region of the diffracted wavefront, the interferometer comprise record working aperture among known PDIs. The interferometer makes it possible to study samples with a reflectance that varies over a wide range. A demonstration of the use of this interferometer for high-precision measurements of a spherical mirror is presented. Sub-nanometer reproducibility of measurements in terms of the peak to valley (PV) parameter and sub-angstrom reproducibility in terms of the rms are demonstrated.

A volume plasmon blueshift in thin silicon films embedded within Be/Si periodic multilayer mirrors.

Microstructural properties of the beryllium (Be) and silicon (Si) in periodic multilayer mirrors Be/Si with the variation of film thickness were comprehensively determined by Raman scattering. For the thinner films, the structure of Be evolved in the amorphous phase, and it was transformed into the polycrystalline phase for thicker films. The Si films in the periodic structure were condensed into the amorphous phase. The small fraction of nanocrystalline Si particles was distributed within the amorphous phase. A shake-up satellite peak of Si 2s photoelectrons was observed in X-ray photoelectron spectroscopy which suggested the excitation of a plasmon in Si films embedded within Be/Si periodic multilayers. The energy of plasmons was sensitive to the film thickness of Si in the periods which directly corresponds to the particle size. The binding energy of the satellite peak of Si 2s photoelectrons was blueshifted (higher energy) with a decrease in the particle size. This was explained by size dependent quantum confinement of particles.

Axisymmetric surface shape correction of optical elements by a wide-aperture ion beam.

Methods for calculating the process of axisymmetric surface shape correction with a wide-aperture ion beam through a forming diaphragm for optical elements with a round and arbitrary border shape are presented. In the case of circular optical elements, an approach based on the separation of the axisymmetric component of the surface shape error from its decomposition by Zernike polynomials is used. In the case of optical elements with an arbitrary border shape (not round), an algorithm for searching the axisymmetric component of the shape error is proposed. The search criterion is to minimize the residual volume of the deviation of the surface shape from the calculated one. The proposed algorithm makes it possible to separate the axisymmetric component of the shape error relative to an arbitrary axis, including one located outside the workpiece. The results of surface treatment in accordance with the above methods are presented.

Phase analysis of tungsten and phonon behavior of beryllium layers in W/Be periodic multilayers.

In periodic W/Be multilayers, thickness-dependent microstructural and phase modifications were investigated in W and Be layers. In X-ray diffraction, α-W was predominant for the ultrathin layer of W, while ß-W evolved along with the α-W phase for higher film thickness. For the thicker layers, the thermodynamically metastable ß-W vanished and a single well-defined preferably oriented stable α-W phase was observed. The lattice spacing revealed that these phases exist in the tensile stressed condition. With the increase in thickness of Be layers, the blueshift and narrow linewidth of the transverse optical (TO) phonon mode was observed in Raman scattering studies. However, the TO mode was redshifted and the linewidth was further narrowed consistently with an increase in the thermal annealing temperature of the multilayers. The investigation has quantified an increase in compressive strain and reduction of defects with an increase in thickness of the Be layers. However, for thermally annealed samples, the compressive strain in the Be layers was relaxed and crystalline quality was improved.

Effect of annealing on the interface formation in Mo/Be multilayer structures without/with a barrier layer.

In the present paper, the formation of an interface region in the multilayer periodic Mo/Be structure with/without a B4C or Si barrier layer depending on the annealing conditions was studied using X-ray photoelectron spectroscopy. The formation of different beryllides at the interfaces Be-on-Mo and Mo-on-Be was explained by the impact of the deposition-induced exchange caused by ballistic collisions and surface free energy. The influence of the high temperatures on the thermal stability of Mo/Be multilayer systems without/with a barrier layer was studied. Since the appropriately selected barrier layers prevent the formation of the interlayer region of mirrors at room temperature, it was concluded that it would also lead to a weakening of interlayer diffusion in multilayer mirrors at higher temperatures. The effect of barrier layer insertion on the thermal stability of Mo/Be structures was analyzed in detail. It was established that regardless of the material, the introduction of a barrier layer: (i) limits the formation of beryllides with an increase in the annealing temperature at the Be-on-Mo interface; (ii) prevents the formation of MoBe2, while forming MoBe12 beryllide at the Mo-on-Be interface; and (iii) does not limit the beryllium oxidation process at the Mo-on-Be interface.

Phonon, plasmon and electronic properties of surfaces and interfaces of periodic W/Si and Si/W multilayers.

The phonon and plasmon excitations and electronic properties of interfaces of periodic W/Si and Si/W multilayer structures were investigated. The Boson band originated from quasilocal surface acoustic phonons for ultrathin Si layers, excited by Raman scattering. In confined Si layers, a small fraction of crystalline Si nanoclusters were embedded within a large volume fraction of amorphous Si (a-Si) nanoclusters. The size of the a-Si nanoclusters was smaller for the thinner Si layer in the periodic layers. The plasmon energy in the Si layer was blueshifted with a decrease in the thickness of this layer. This was explained by the size-dependent quantization of plasmon shift. The valence band spectra comprised a substantial fine structure, which is associated with the interaction of valence orbitals of the W and Si atoms at the interface boundaries. For thinner Si layers, the binding interaction of W5d and Si3p states leads to the splitting of the density of states near the Fermi level in the energy range of 1.5-5 eV. However, the energy splitting with two maxima was observed at 0.7 and 2.4 eV for thicker layers. Thus, the results of X-ray photoelectron spectroscopy have indicated that the interface of W/Si multilayers consists of metal-enriched tungsten silicide. Both the atomic structure and the elemental composition of the silicide were modified with a change in the thickness of the Si layers. This novel investigation could be essential for designing nanomirrors with higher reflectivity.

Inhibition of chemical interaction of molybdenum and silicon in a Mo/Si multilayer structure by the formation of intermediate compounds.

In the present study, the formation of intermediate compounds in the Mo/Si multilayer was realized by the introduction of barrier layers at the interfaces. Their impact on the interdiffusion of Mo and Si was analyzed via X-ray photoelectron spectroscopy. It was established that the insertion of a thin Be barrier layer led to the formation of beryllide MoBe12 at the interface Si-on-Mo, which prevented the formation of molybdenum disilicide and improved the interface. The insertion of the B4C barrier layer led to its complete decomposition with the formation of borides and carbides of molybdenum and silicon (MoBx, SiBx, MoxC and SiCx) at the Si-on-Mo interface. The formation of only MoBx and SiCx was detected at the Mo-on-Si interface. It was important that the insertion of a thin B4C barrier layer did not fully prevent the formation of MoSi2 at both (Si-on-Mo and Mo-on-Si) the interfaces. These facts allowed us to assume that the diffusion barrier function of the B4C interlayer could be caused by the stability of the formed compounds, rather than the stability of the B4C layer itself.

Optical constants of sputtered beryllium thin films determined from photoabsorption measurements in the spectral range 20.4-250†eV.

In this work, the refractive index of beryllium in the photon energy range 20.4-250 eV was experimentally determined. The initial data include measurements of the transmittance of two free-standing Be films with thicknesses of 70 nm and 152 nm, as well as reflectometric measurements of similar films on a substrate. Measurements were carried out at the optics beamline of the BESSY II synchrotron radiation source. The absorption coefficient ß was found directly from the transmission coefficient of the films, and the real part of the polarizability δ was calculated from the Kramers-Kronig relations. A comparison is carried out with results obtained 20 years ago at the ALS synchrotron using a similar methodology.

Angle resolved photoelectron spectroscopy as applied to X-ray mirrors: an in depth study of Mo/Si multilayer systems.

We present an approach adapted to study the interface (composition and extension) of X-ray multilayer mirrors using angle resolved photoelectron spectroscopy (ARXPS). In the approach we rely on the concept of the average effective attenuation length (EAL) of the photoelectron and not on the inelastic mean free path (IMPF), which allows us to take into account the contribution of elastically scattered electrons and to increase the accuracy of the determined thickness of the layers. We apply the developed approach to study the formation of interfaces in a multilayer periodic Mo/Si mirror. The chemical composition and significance of the interfaces depending on the number of periods were investigated by means of the ARXPS spectra decomposition technique. Formation of a molybdenum silicide MoSi2 at the interfaces was revealed. It was shown that molybdenum silicide with different thicknesses is formed at the interfaces depending on the film order. In addition, it was established that increasing the period number of the [Mo/Si] system leads to a decrease of the interface extension.

A method of z-tomography using high-aperture soft X-ray microscopy.

Multilayer normal-incidence mirrors allow the numerical aperture (NA=0.3-0.5) of a projection lens to be significantly increased in the spectral ranges of the water (λ = 2.3-4.4 nm) and carbon (λ = 4.4-7 nm) windows, in comparison with the Fresnel zone plates. The low depth of focus of high-aperture optics (tens of nm) makes it possible to use z-tomography to reconstruct the structure of samples in soft X-ray microscopy. The presence of strong absorption prevents the direct use of a powerful deconvolution apparatus developed for fluorescence optical microscopy to improve the clarity of the image. In this article, the "intensity restoration algorithm" is proposed that takes into account the absorption effect before standard deconvolution. For an imagine lens with NA = 0.3 and a working wavelength of 3.37 nm, the results of simulating an image of a protein cell and its deconvolutionary processing are presented, before and after applying the proposed method. After its application, the deconvolution efficiency is significantly increased. A "full-period" resolution of 40 nm was obtained for the image of a simulated protein cell.